This invention relates to coated particles and more particularly to particles having a conformal coating thereon. More particularly, this invention relates to phosphors and still more particularly to electroluminescent phosphors having thereon a coating that protects the phosphor from moisture absorption and greatly increases the life and efficacy.
Coated phosphors are known from U.S. Pat. Nos. 4,585,673; 4,828,124; 5,080,928; 5,118,529; 5,156,885; 5,220,243; 5,244, 750; and 5,418,062. It is known from some of the just-mentioned patents that a coating precursor and oxygen can be used to apply a protective coating. See, for example, U.S. Pat. Nos. 5,244,750 and 4,585,673. The coating processes in several of the others of these patents employ chemical vapor deposition to apply a protective coating by hydrolysis. Additionally, U. S. patent application Ser. No. 03/153,978, filed Sep. 16, 1998, now abandoned and assigned to the assignee of the present invention, the teachings of which are hereby incorporated by reference, discloses a method for coating phosphor particles by chemical vapor deposition and using an oxygen/ozone reactant. The latter process operates in the absence of water or water vapor. It would be a further advance in the art to increase the efficacy and the life of such coated phosphors even more.
It is, therefore, an object of the invention to obviate the disadvantages of the prior art.
It is another object of the invention to enhance the operation of coated phosphors.
Yet another object of the invention is the provision of a phosphor coating method that does not employ water or water.
These objects are accomplished, in one aspect of the invention, by a method of coating phosphor particles by introducing an inert gas into a reaction vessel; charging phosphor particles into the reaction vessel to fluidize the same; heating the reaction vessel to a reaction temperature; introducing a precursor into said reactin vessel and maintaining the temperature for a time sufficient to saturate the phosphor particles with the precursor; introducing further precursor into the reaction vessel; introducing an oxygen/ozone mixture into the reaction vessel; and maintaining the inert gas flow, oxygen/ozone mixture flow and further precursor supply for a time sufficient to coat the phosphor particles.
The process yields lamps with lives in excess of 1000 hours with efficacies in excess of 5.3 lumens per watt (lm/watt) and 24 hour light output above 23 foot-lamberts.
For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims.